This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Quantitative DSC-MRI perfusion imaging requires signal values that can be accurately converted to tracer concentration values but measuring vascular concentration (e.g. arterial input function AIF) remains challenging. Susceptibility agents induce a change in the resonance frequency that is linear with the tracer concentration and does not depend on T1. This change in frequency can be assessed by change in MR signal phase and could potentially deliver better estimates of tracer concentration. The observable phase effect depends however on the orientation of the vessels relative B0 (Eq. 1) and information about vessel orientation is thus warranted. To avoid extra cumbersome measurements we propose to estimate the vessel orientation from the magnitude data of the dynamic EPI scan itself. To read about other projects ongoing at the Lucas Center, please visit http://rsl.stanford.edu/ (Lucas Annual Report and ISMRM 2011 Abstracts)